1. Field
The present disclosure relates to a color image sensor, and more particularly, to a color image sensor free from a color filter.
2. Description of the Related Art
Referring to FIG. 1a, a color image sensor widely used in the art has a combination of a photo-sensitive cell array and a color filter array. The color filter array filters light of a specific color (wavelength) in an optical way, and the filtered light is sent to a photo-sensitive cell to measure a photoelectric transformation voltage or photoelectric transformation current according to the intensity of the light so as to determine the color and intensity of the light incident to a pixel. However, in this method, a color filter is required since the response of the photo-sensitive cell is not sensitive to the color of light, and for this reason, the production cost is high. In addition, since the color filter array has a horizontal arrangement, the minimum size of the pixel should be greater than a certain level, resulting in a bad resolving power of an image.
To solve this problem, U.S. Pat. No. 7,233,036 B1 and ┌Yves Audet, et al., “A CMOS Process Compatible Color Sensor using Wavelength Dependent Absorption Depth”, IEEE, 2008, pp. 327˜330┘ have proposed a configuration where a triple PN junction photoelectric transformation element is disposed according to the depth as shown in FIG. 1b. In this technique, by using the difference in skin depths according to the wavelength, electric signals generated from photoelectric transformation elements are detected to determine the wavelength of incident light, namely the color and intensity of light. However, since this technique needs complicated photo-lithography and ion implantation processes to form the triple PN junction, and therefore the production cost is high.